I have looked through the board and still am not sure about my situation. Namely how to deal with existing 3 phase power to my current unit.

I have a 5 ton 15 yo Trane AC with 3 phase AC. I know that is uncommon for residential, but maybe its because this is an older house in Phoenix? I cant tell you the colors of the wires right now but there are three contacts in the disconnect box. I have not put my volt meter on it either.

I live in Phoenix so the efficiency of a new unit makes sense at the higher SEER ranges. We plan to live here for 10+ more years.

I have three bids, all with load calcs and two of the firms seem to be excellent contractors. All three recommended the XL19i.

Of the two remaining contractors, one wants to have a new single phase line run from across the yard (no attic access) which means trenching and alot of labor. The other company feels they can convert the existing 3 phase supply to single phase.

Has anyone had experience with this? I guess I will ask for my own electrician to look at this as well, but if I can avoid thousands of dollars to run a new single phase line it certainly would be nice.